Synthesis, Structure and Luminescence of High Brightness Gallium Nitride Powder
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SYNTHESIS, STRUCTURE AND LUMINESCENCE OF HIGH BRIGHTNESS GALLIUM NITRIDE POWDER R. Garcia, A. Thomas1, A. Bell, M. Stevens, and F. A. Ponce Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85281-1504 1 Technology Development, Roger Corporation, Durel Division, Chandler, AZ 852246155 ABSTRACT Highly luminescent GaN powders have been synthesized by reacting high purity gallium metal with ultra-high purity ammonia in a horizontal quartz reactor at 1100 ºC. The powders produced in this reactor consist of light grey micro-crystals with wurtzite structure. Elemental analysis indicates that the powders obtained by this method have a high nitrogen concentration (more than stoichiometric GaN, 16.73 weight %). Powder X-ray diffraction demonstrates that the material has a high purity and single crystalline structure. Electron microscopy shows that the powders consist of at least two kinds of particles, small sized platelets and large sized needles. The resulting GaN powders are thousands of times more cathode- and photo-luminescent than other GaN powders including commercially available material. Their luminescence intensities are comparable to that of GaN thin films grown by hydride vapor phase epitaxy and metal organic chemical vapor deposition. INTRODUCTION Much interest currently exists in the group III-nitride semiconductors because of their use in high power electronic and optoelectronics, such as flat panel displays, light emitting diodes, and laser diodes [1]. While most of the GaN materials are produced as thin films, GaN powders have potential applications as electroluminescent phosphor. The first reported synthesis of GaN powder was achieved in 1932 [2] by flowing ammonia over molten gallium heated between 900 – 1000 ºC, following the reaction: 2 Ga(s) + 2 NH3(g) 2 GaN(s) + 3 H2(g) Subsequent research in 1972 confirmed the efficiency of this process route [3], reporting reaction at 1150 ºC on the surface of the melt, after a few minutes, with the formation of gray gallium nitride. Because of the remaining gallium melt under the crust of GaN, this approach requires several stages in order to achieve full reaction. Impurities such as residual gallium metal and gallium oxide are typically present in the as-synthesized material, affecting its optoelectronics properties [4-10]. We have developed an improved approach to produce GaN powder using the same reaction as above. This approach leads to highly luminescent GaN powders. Thermodynamic calculations using recently published thermochemical data [11] predicts a complete reaction at 1100 ْC with a free energy of -99.52 kJ/mol and a enthalpy of 111.446 kJ/mol. We have produced large amounts of stoichiometric GaN powder (~10 grams/batch) in a horizontal reactor, using ultra-high purity precursors (gallium 99.9995
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weight % and ammonia 99.9995 weight %) and highly controlled parameters (temperature, pressure, gas-flow and time). GaN powders have many possible applications including electroluminescent lamps in appliances such as
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